Spinal surgery apparatus and method

ABSTRACT

An apparatus for implementing an improved spinal fusion cage have a centrally-located fixation screwhole of diameter minimized to accommodate a variable-angle, intervertebral, cannulated fixation screw is disclosed. The system includes a rigid connection between the spinal fusion cage to the shaft of the fixation screw, and a variable angle drill targeting device for directing the fixation screw through the on-visually acquirable, centrally-located fixation screwhole without X-ray or other imaging guidance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This international application claims priority to U.S. application Ser.No. 13/388,993, filed on Feb. 5, 2012, which in turn claims priority toInternational Application No. PCT/US2010/055531, filed on Nov. 5, 2010,which in turn claims priority to U.S. Provisional Application No.61/280,621, filed on Nov. 6, 2009, where the entire contents of allapplications are incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates generally to a surgical apparatus, and aprocedure and method for using that apparatus.

BACKGROUND OF THE INVENTION

A spinal fusion is a surgical procedure that promotes two back bones, orvertebrae, growing together into one bone. FIG. 1 models the front oranteroposterior view of two such vertebrae L5 (104) and S1 (108)separated by a disc 112. FIG. 2 models the side or lateral view of thesame. As shown in FIG. 3, in the course of the spinal fusion, a fusioncage 304 is at times required.

The fusion cage 304 is a medical implant that is used to replace theremoved disc between two vertebrae or to replace one or more vertebraeand their adjacent disc. Fenestrations 308 in these cages are usuallyfilled with a bone grafting material that promotes a bony fusion betweenthe bone above the cage and the bone below the cage. A screwhole 312 isusually provided in the front of the cage to accommodate an insertionhandle used in positioning the cage into the disc space. Fusion cagesare supplied in various sizes to fit the space between the bones beingfused. As shown in FIG. 4, a trial cage 404 can be used to select thedesired size fusion cage to fit into the disc space.

In some situations it is desirable to mechanically fix together thebones above and below the cage in order to limit movement between thebones and cages, thus promoting successful fusions and preventing cagedisplacement. This fixation can be accomplished as shown in FIG. 5 bypassing a guide pin 504 into the bone on the near side of the cage,through a fenestration 308 in the interior of the fusion cage 304, andthen into the bone on the far side of the cage. A fixation screw 508 canthen be inserted over the guide pin 504 after which the guide pin isthen removed. As FIG. 6 illustrates, the cage fenestration 308 cannot bevisually acquired with the cage 304 in place in the disc. The trajectoryof the guide pin 504, starting from the visually acquired guide pinentry point 604, must instead be directed with the use of x-rays.

In order to visualize the location of the cage fenestration 308 (FIG. 5)through which a fixation screw 508 is to pass, metal markers are placedin the wall of the fusion cage 304 that are immediately adjacent to thisfenestration 308.

FIG. 7 illustrates the front view of the spine shown in FIG. 6 as itwould appear on an x-ray. The L5 backbone 104 and S1 backbone 108 wouldbe seen. Since the fusion cage 304 and the remaining disc 112 areinvisible on x-ray, an empty space would appear in their place. Because,like bone, metal is visible on x-ray, metal markers in the walls of thecage fenestration 308 would be visible. The surgeon would be able toacquire the right side wall marker 704 and the left side wall marker708.

FIG. 8 illustrates the side view of the spine pictured in FIG. 6 as itwould appear on an x-ray. The L5 backbone 104 and the S1 backbone 108would be visible. Again, an empty space would appear in the place offusion cage 304 and any remaining disc 112. On the x-ray, the surgeonwould be able to acquire the additional front wall marker 804 and therear wall marker 808. As depicted in FIG. 8, these markers can be madein a different shape in order to distinguish them from the side wallmarkers 704 and 708 shown in FIG. 7.

Being metallic, the guide pin 504 can also be seen on an x-ray. Usingthe front x-ray view exemplified by that shown in FIG. 7, a surgeonwould direct the guide pin 504 between the right side wall marker 704and the left side wall marker 708. Using the side x-ray view FIG. 8, thesurgeon simultaneously directs the guide pin 504 between the front wallmarker 804 and the rear wall marker 808.

The surgeon would thus be assured that s/he has passed the guide pin 504through the L5 backbone 104, through the cage fenestration 308 in thefusion cage 304, and into the S1 backbone 108. The surgeon can theninsert the fixation screw 508 down over the guide pin 504 as shown inFIG. 7 and FIG. 8. The guide pin 504 would then be removed, leaving thefixation screw 508 in position passing through the cage fenestration 308in the fusion cage 304.

Unfortunately, due to the difficulty in directing a guide pin 504through a screwhole fenestration 308 in a fusion cage 304 using x-rays,the screwhole fenestration 308 must be significantly larger than thefixation screw 508. As a result, it is possible for the fusion cage 304to partially displace out of the disc 112. This displacement can thenresult in excessive movement between the L5 backbone 104 and the S1backbone 108, resulting in a failure of the spinal fusion. As shown inFIG. 5, a large screwhole fenestration 308 leaves any remainingfenestrations in the fusion cage 304 to be small. This results in mostof the bone grafting material being placed in the screwhole fenestration308, which is unwanted.

Further, passage of the fixation screw 508 through the screwholefenestration 308 can disturb this bone grafting material and adverselyimpact a successful spinal fusion. It is therefore desirable to make thescrewhole fenestration 308 as small as possible in order to prevent cagemigration, and to allow the remaining fenestrations to be as large aspossible and to carry the majority of the bone grafting material.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus andmethod for performing specific types of spinal surgeries. The apparatusand method assist in permanently locating a fusion cage within a spine.It is an additional object of the present invention to make the surgicalprocedures easier and safer to perform. These and other objects andadvantages of the invention will become readily apparent as thefollowing description is read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show front and side views, respectively, of two vertebrae;

FIG. 3 shows an example fusion cage;

FIG. 4 shows an example trial cage;

FIG. 5 shows an example guide pin and fixation screw within a fusioncage such as that shown in FIG. 3;

FIG. 6 shows a view of a spine with a fusion cage inserted therein;

FIGS. 7 and 8 show the front and side views of the spine shown in FIG.6;

FIGS. 9A, 9B, 9C, and 9D show, respectively, plan, front, right-side,and cross-sectional right-side views of a modified fusion cage;

FIG. 9E shows the modified fusion cage of FIGS. 9A-9D including frontand rear trajectories;

FIG. 9F shows the modified fusion cage of FIGS. 9A-9E including rightand left trajectories;

FIG. 10A shows a plan view and cross-sectional right side view of asecond version of a modified fusion cage;

FIG. 10B shows a snap ring incorporating an anti-spin tab which fitsinto the anti-spin recess within the modified fusion cage of FIG. 10A;

FIGS. 10C, 10D, 10E, and 10F illustrate a snap ring within the modifiedfusion cage of FIGS. 10A-10B;

FIG. 11A shows a rigid drill targeting device;

FIGS. 11B and 11C show a drill target inserted through a utilityscrewhole in a modified fusion cage;

FIG. 12A shows a left side view of an articulating drill targetingdevice;

FIG. 12B shows an example of an insertion handle that screws into amodified fusion cage;

FIG. 12C shows a back view of the articulating drill targeting device ofFIG. 12A;

FIG. 12D shows a left side view and a cross-sectional view of a guidebody;

FIGS. 12E-12F show back and front views, respectively, of the guide bodyof FIG. 12D;

FIG. 12G shows an exploded perspective view of the guide body of FIGS.12D-12F;

FIG. 12H shows a drill guide having depth gauge markings and numbers,and a flexible guide pin tissue protector that can be screwed onto orotherwise attached to the drill guide;

FIG. 12I shows a flexible screw insertion tissue protector that can beslid over a guide pin;

FIG. 13 depicts a potential method for implementing the preferredembodiments;

FIG. 14 shows excising a diseased disc, thus creating a space for acage;

FIG. 15 shows trialing the disc space of FIG. 14 by attaching the trialcage to an insertion handle;

FIG. 16 shows inserting a modified fusion cage into a space using aninsertion handle;

FIG. 17A shows an example position of a rigid drill targeting devicerotated to the left side;

FIG. 17B shows the rigid drill targeting device of FIG. 17A rotated tothe right side;

FIGS. 17C and 17D shows the rigid drill targeting device rotated towardthe front and back directions, respectively;

FIG. 17E-17H show example positions of an articulating drill targetingdevice;

FIG. 18 illustrates obtaining an example measurement for a fixationscrew length;

FIG. 19 shows an example use of a guide pin operated in conjunction withthe articulating drill targeting device of FIGS. 17E-17H;

FIG. 20 shows an example removal of the articulating drill targetingdevice of FIGS. 17E-17H;

FIG. 21 shows an example insertion of a fixation screw;

FIG. 22 shows an example of the fixation screw of FIG. 21 being in afinal position; and

FIG. 23 shows an example of the fixation screw of FIGS. 21-22 beinglocked.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before explaining the disclosed embodiment of the present invention indetail it is to be understood that the invention is not limited in itsapplication to the details of the particular arrangement shown, sincethe invention is capable of other embodiments. Also, the terminologyused herein is for the purpose of description and not of limitation.

The embodiments disclosed herein involve the use of a rigid drilltargeting device 1104 such as that shown in FIG. 11A or an articulatingdrill targeting device 1204 such as shown in FIG. 12A combined with amodified fusion cage 904 FIG. 9A, or with a modified fusion cage 1004FIG. 10A. As noted earlier, a fusion cage is a medical implant that isto be permanently installed within a human spine. The targeting devicesdisclosed herein and other elements are combined to direct a guide pin504 (e.g. FIG. 8) along the desired trajectory for placing a screwthrough the bone on the near side of the modified fusion cage 904 ormodified fusion cage 1004, through a fixation screwhole 914 in modifiedfusion cage 904 (e.g. FIG. 9A) or a fixation screwhole 1014 in amodified fusion cage 1004 (e.g. FIG. 10A), and into the bone on the farside of the modified fusion cage 904 or modified fusion cage 1004. Thedrawings herein illustrating the various embodiments generally show tothe L5 and S1 vertebrae. However, it is to be noted that the L5 and S1vertebrae are but examples, for illustration only. The embodimentsdiscussed herein can also be used on other combinations of vertebraebesides those explicitly shown in the drawings.

A first advantage is that X-ray guidance of the guide pin 504 is notrequired. The improved accuracy of insertion of guide pin 504 allows thefixation screwhole 914 or fixation screwhole 1014 to be made in adiameter that is near or the same as that of the fixation screw 508.

A second advantage is that the risk of cage migration is eliminated. Theremaining cage fenestrations can be made as large as possible and willcontain all of the bone grafting material. There is no bone graftingmaterial to be disturbed by the insertion of the fixation screw 508.

FIG. 9A shows the plan view of a modified fusion cage 904 having a front906, back 908, right side 910, and left side 912. A centrally-locatedfixation screwhole 914 accommodates passage of a guide pin 504 followedby a fixation screw 508 as was illustrated at least within FIGS. 7 and8. As shown in FIG. 9A, additional fenestrations 308 accommodate bonegrafting material.

FIG. 9B shows the front view of the modified fusion cage 904incorporating a utility screwhole 920 which connects with the fixationscrewhole 914. FIG. 9C shows the right side view of the modified fusioncage 904 with the taller front 906 and shorter back 908 which fit thetapered shape of disc 112 that the modified fusion cage 904 replaces.FIG. 9D shows the cross-sectional right side view of the modified fusioncage 904 illustrating an hourglass shape of the fixation screwhole 914.Also shown is the connecting utility screwhole 920.

FIG. 9E shows how this hourglass shape is necessary if the fixationscrewhole 914 is to be made the smallest diameter possible yet stillaccommodate a fixation screw 508 being inserted along a trajectory whichcan vary through arc 924 from a maximum front trajectory 926 to amaximum rear trajectory 928.

Also illustrated within FIG. 9E is how the connecting utility screwhole920 can accommodate the insertion of a locking screw 930 which canengage the fixation screw 508 and prevent it from subsequently migratingin or backing out of the fixation screwhole 914. In FIG. 9F, across-sectional front view of the modified fusion cage 904 shows howthis same hourglass shape keeps the diameter of the fixation screwhole914 to a minimum while accommodating a fixation screw 508 being insertedalong a trajectory which can vary from a maximum left trajectory 936,through an arc 934, to a maximum right trajectory 938.

FIG. 10A shows a plan view and cross-sectional right side view of asecond version of a modified fusion cage 1004 having the same featuresas the modified fusion cage 904, except for a further modification offixation screwhole 914 resulting in the fixation screwhole 1014. Thisfixation screwhole 1014 includes a bearing or snap ring recess 1016which accommodates a tilting bearing or snap ring 1018. The bearing orsnap ring recess 1016 may incorporate an anti-spin recess 1017.

FIG. 10B shows the snap ring 1018 incorporating an anti-spin tab 1019which fits into the anti-spin recess 1017 located at the back of thebearing or snap ring recess 1016. The anti-spin recess is sufficientlylarge to allow the bearing or snap ring 1018 to tilt in the bearing orsnap ring recess 1016, but small enough to prevent the bearing or snapring 1018 spinning while fixation screw 508 is being inserted. Thebearing or snap ring 1018 incorporates a central screwhole 1020 which isthe same diameter as the fixation screw 508.

This same anti-spin feature maybe accomplished by making the bearing orsnap ring recess 1016 non-circular in shape and making the bearing orsnap ring 1018 have a matching non-circular outer shape.

While the hourglass shape of the fixation screwhole 914 in the modifiedfusion cage 904 reduces the diameter of the fixation screwhole 914 to aminimum, screw passage from a variety of angles as described at leastwithin FIGS. 9E and 9F results in the minimum diameter at the waist ofthe hourglass-shaped fixation screwhole 914 still being slightly largerthan the diameter of the fixation screw 508.

Undesired residual movement between the modified fusion cage 904 and thefixation screw 508 can be further reduced or eliminated by the lockingscrew 930. FIGS. 10C, 10D, 10E, and 10F illustrate how use of thetilting bearing or snap ring 1018 in the modified fusion cage 1004achieves a fixation screwhole 1014 having a minimum diameter exactlymatching the diameter of the fixation screw 508.

FIG. 10C shows a cross-sectional right side view of the modified fusioncage 1004. The fixation screw 508 is being inserted along the maximumfront trajectory 926. As the fixation screw 508 starts to thread itselfthrough the central screwhole 1020 in the bearing or snap ring 1018, thebearing or snap ring 1018 will tilt to the front until it becomesperpendicular to the fixation screw 508.

Since the inner diameter of the bearing or snap ring 1018 matches theouter diameter of the fixation screw 508, there is no side-to-sidemovement possible between the two. Further, since the outer dimension ofthe tilting bearing or snap ring 1018 matches the inner dimension of thebearing or snap ring recess 1016, there is no side-to-side movementpossible between these two either. The combined result ensures that noside-to-side movement is possible between the fixation screw 508 and themodified fusion cage 1004. As in the modified fusion cage 904, thelocking screw 930 can then be inserted into the utility screwhole 920 toengage the fixation screw 508 and prevent its migrating in or backingout of the fixation screwhole 1014.

FIG. 10D shows the tilting bearing or snap ring 1018 tilted to the backaccommodating insertion of a fixation screw 508 along the maximum backtrajectory 928. Similarly, the cross-sectional front views at leastwithin FIGS. 10E and 10F illustrate how the tilting bearing or snap ring1018 can tilt respectively left accommodating the maximum lefttrajectory 936 or right accommodating the maximum right trajectory 938for insertion of the fixation screw 508.

The tilting snap ring 1018 can be made with the diameter of the centralhole 1020 (e.g. FIG. 10B) slightly smaller than the outer diameter ofthe fixation screw 508 and with the outer dimension of the snap ring1018 similarly smaller than the inner dimension of the bearing or snapring recess 1016. As the fixation screw 508 advances into the tiltingsnap ring 1018, the central hole 1020 will expand to the outer dimensionof the fixation screw 508. The outer dimension of the snap ring 1018will similarly expand to the inner dimension of the bearing or snap ringrecess 1016. When the fixation screw 508 is in its final position, itcan still be gripped tightly enough by the expanded snap ring 1018 tomake the locking screw 930 unnecessary.

As shown in FIG. 5, insertion of a guide pin 504 through a largefenestration 308 using x-ray guidance can be challenging for thesurgeon. Bringing an x-ray machine into the operative field requires thesurgeon and his assistants to move out of the way while still trying tohold retractors and sharp instruments, such as guide pin 504, inposition.

As shown in FIG. 7, excellent hand-eye coordination is required for thesurgeon to look at the relative position of the fusion cage 304, asdenoted by the right side marker 704 and left side marker 708, and theguide pin 504 on the front x-ray view of the spine. The trajectory ofthe guide pin 504 in this side-to-side direction must be adjustedaccordingly. The surgeon must then maintain the guide pin 504 in thisexact position while the x-ray machine is re-positioned to expose theside view of the spine as shown in FIG. 8. Additional movement ofsurgeon and assistants maybe required to accommodate this repositioningof the x-ray machine. The surgeon must again rely on good hand-eyecoordination while he looks at the side x-ray view of the spine andadjusts the trajectory of the guide pin 504 in this front-to-backdirection before advancing the guide pin 504 into the backbone 104.

The surgeon then stops advancing the guide pin 504 and repeats the frontand side x-rays and makes further adjustments to the trajectory. Thesefurther adjustments can be difficult because the guide pin 504 must bepulled back almost out of the backbone 104 before it can be re-directed.When then advanced in the corrected direction, the guide pin 504 maydeflect back down the previous mis-aligned drill path. The guide pin 504may then have to be completely removed from the back bone 104 and a newentry site for guide pin insertion selected. The entire previouslydescribed guide pin insertion process must then be started all overagain.

While the placement depicted in FIG. 5 of a guide pin 504 through alarge fenestration 308 in fusion cage 304 using the described x-rayguidance method is challenging, it is still possible in the hands of asufficiently skilled surgeon. Conversely, the placement of a guide pin504 through a minimal diameter fenestration, such as the fixationscrewhole 914 in the modified fusion cage 904 or the fixation screwhole1014 in modified fusion cage 1004, using the described x-ray guidancemethod, is sufficiently difficult as to be impractical. Consequently, inorder to achieve the benefits of the tight fit between fixation screw508 and modified fusion cage 904 or modified fusion cage 1004, analternative guidance method for placement of the guide pin 504 isrequired.

As shown in FIG. 11A, a rigid drill targeting device 1104 consists of asmall sliding pipe or drill guide 1108 mounted in a guide body 1120. Adrill arm 1112 connects a semi-circular drill target 1116 to the guidebody 1120. The sliding drill guide 1108 is secured by a thumbscrew 1118.The drill guide 1108 directs the guide pin 504 precisely through thenotch in the drill target 1116 on the opposite end of the drill arm1112.

FIGS. 11B and 11C show how the drill target 1116 can be inserted throughthe utility screwhole 920 in the modified fusion cage 904 to engage thefront side of fixation screwhole 914. With the drill target 1116 thuspositioned, the guide pin 504 is directed by the drill guide 1108precisely through the center of the fixation screwhole 914.

The rigid drill targeting device 1104 can be rotated front-to-back whilemaintaining the drill target 1116 aligned in the center of the fixationscrewhole 914. The trajectory of the guide pin 504 can thus be variedthrough a front-to-back arc 924 as depicted at least within FIG. 9E.

As depicted in FIG. 9F the rigid drill targeting device 1104 can also berotated side-to-side while maintaining the drill target 1116 aligned inthe center of the fixation screwhole 914. The trajectory of the guidepin 504 can thus be varied through the side-to-side arc 934.

In either variation of trajectory, the rigid drill targeting device 1104will maintain the direction of the guide pin 504 precisely through thecenter of the fixation screwhole 914.

The drill target 1116 can similarly be placed through the utilityscrewhole 920 in modified fusion cage 1004 (e.g. FIG. 10A) to engage thefront side of the central hole 1020 of rotating bearing or snap ring1018 (e.g. FIG. 10B). The guidance benefits describe for placing a guidepin 504 through the fixation screwhole 914 in modified fusion cage 904can also be achieved for the fusion cage 1004.

By using the rigid drill targeting device 1104, x-ray guidance is notrequired and therefore movement of surgeon and assistants away from theoperative field is not required. Also, it is not required that thesurgeon have extraordinary hand-eye coordination or exceptional skill.Also, operative time for placing the guide pin 504 is reduced.Eliminating the x-ray machine from the operative field and reducing theoperative time combine to reduce the likelihood of wound contaminationand infection.

The placement of a fixation screw 508 in a minimum diameterfenestration, such as fixation screwhole 914 in modified fusion cage 904or fixation screwhole 1014 in modified fusion cage 1004, can beaccomplished with repeatable speed and precision and with relative ease.The benefits of a tight fit between fixation screw 508 and modifiedfusion cage 904 or modified fusion cage 1004 can thus be realized.

As depicted in FIG. 11B, movement of the rigid drill targeting device1104 in the front-to-back direction is limited by the diameter andlength of the utility screwhole 920 relative to the diameter of thedrill arm 1112. Rotation of the drill targeting device 1104 toward thefront of the modified fusion cage 904, when trying to achieve themaximum front trajectory 926 (e.g. FIG. 9E), can be stopped short by thedrill arm 1112 contacting the bottom side of the utility screwhole 920.Similarly, a rotation of the rigid drill targeting device 1104 towardthe back of the modified fusion cage 904, when trying to achieve themaximum back trajectory 928 (e.g. FIG. 9E), can be stopped short by thedrill arm 1112 contacting the top side of the utility screwhole 920.When this happens, the available arc 924 (FIG. 9E) for varying thetrajectory of a guide pin 504 in the front-to-back direction is reduced.In turn the ability of the surgeon to pick his desired entry point intoa backbone 104 (e.g. FIG. 8), and thus to avoid important adjacentanatomical structures, is reduced.

Additionally, as the drill arm 1112 passing through the utilityscrewhole 920 is made smaller in diameter, the available arc 924 (e.g.FIG. 9E) is increased. The likelihood, however, of inadvertently bendingthe drill arm 1112 increases. A bent drill arm 1112 would result in amis-direction of the guide pin 504.

Further, the drill target 1116 can inadvertently slip off of itsengagement on the front side of the fixation screwhole 914 (e.g. FIG.11B) or on the front side of the central hole 1020 in the rotatingbearing or snap ring 1018 (e.g. FIG. 10B). Such a disengagement, if notrecognized by the surgeon, could result in a mis-direction of the guidepin 504.

As shown in FIG. 11A, the rigid drill targeting device 1104 has theadvantage of simplicity of construction. It also has the advantage ofrigidity of its components which best maintains the alignment of thedrill guide 1104 with the drill target 1116 following repeated use.However, while much better than no targeting device, the previouslydescribed design limitations of the rigid drill targeting device 1104somewhat reduce its utility. Consequently, an alternative targetingdevice that overcomes these limitations is desirable.

FIG. 12A shows the left side view of an articulating drill targetingdevice 1204. At the front is a drill guide 1208 that slides in a guidebody 1212 and is secured by a locking lever 1216. The guide body 1212 islinked to an inserter body 1220 at the bottom by two horizontal arms1224 at the top and by two vertical arms 1228 at the back of theinstrument. All arm connections are made with hinge pins 1232.

The articulating drill targeting device 1204 is used in conjunction witha modified fusion cage 904 or a modified fusion cage 1004, an insertionhandle 1236, a spacer sleeve 1240, a driver cap 1244, and a guide pin504.

As shown in FIGS. 12A and 12B, an insertion handle 1236 is screwed in toa modified fusion cage 904 or into a modified fusion cage 1004 using anopen-end wrench applied to the hex section 1252. The articulating drilltargeting device 1204 is slid down the insertion handle 1236 by way of ahole 1248 through the inserter body 1220 until it abuts the hex section1252 of the insertion handle 1236. A spacer sleeve 1240 slides over theinsertion handle 1236 and abuts the inserter body 1220. A driver cap1224 is screwed onto the insertion handle 1236 and abuts the spacersleeve 1240.

The inserter body 1220 is thus maintained firmly in the desired positionrelative to the modified fusion cage 904 or modified fusion cage 1004.As FIG. 12A shows, the drill guide 1208 directs a guide pin 504precisely along the trajectory 1256 through the center of the fixationscrewhole 914 in modified fusion cage 904 or the fixation screwhole 1014in modified fusion cage 1004.

The articulating drill targeting device 1204 is in the geometricconfiguration of two interconnected parallelograms as defined by thehorizontal arms 1224 and guide body 1212 interconnected by hinge pins1232 to the vertical arms 1228 and the inserter body 1220. Utilizingthis parallelogram principal, the articulating drill targeting device1204 can be rotated front-to-back while maintaining the guide pin 504 inprecise alignment with the center of the fixation screwhole 914.

The further described embodiments of the articulating drill targetingdevice 1204 when used with modified fusion cage 904 are identical whenused with fusion cage 1004.

As shown in FIG. 12A, when rotated toward the front of modified fusioncage 904, the articulating drill targeting device 1204 can easilyachieve the alignment of the guide pin 504 along the maximum fronttrajectory 926 without impediment. Similarly, rotation of thearticulating drill targeting device 1204 toward the back of the modifiedfusion cage 904 achieves alignment of guide pin 504 with the maximumback trajectory 928 without impediment.

As FIG. 12A illustrates, the articulating drill targeting device 1204 isconnected to the modified fusion cage 904 by the robust insertion handle1236. There is no small diameter drill arm 1112 (e.g. FIG. 11B) as usedin the rigid drill targeting device 1104 that is at risk of becomingbent and misguiding a guide pin 504.

As shown in FIGS. 12A and 12B, the screw connection of insertion handle1236 to the fusion cage 904 maintains the articulating drill targetingdevice 1220 to be securely attached to modified fusion cage 904. Aninadvertent disengagement between the targeting device and cage, as canoccur with the rigid drill targeting device 1104, is thus avoided.

FIG. 12C shows the back view of the articulating drill targeting device1204 with the horizontal arm 1224 and the vertical arms 1228 connectedwith the hinge pins 1232 to the guide body 1212 and the inserter body1220. The articulating drill targeting device 1204 slides onto theinsertion handle 1236 using hole 1248 in the inserter body 1220. Drillguide 1208, and therefore guide pin 504, are aligned with hole 1248 asdepicted by guide pin trajectory 1256 (also shown at least within FIG.12A).

As shown in FIGS. 9B and 10A, when insertion handle 1236 is screwed intoutility screwhole 920 in modified fusion cage 904, insertion handle 1236becomes aligned with the center of fixation screwhole 914. With thedrill guide 1208 being in alignment with hole 1220 as shown in FIG. 12C,drill guide 1208 is thus also in alignment with insertion handle 1236and, therefore, also in alignment with the center of fixation screwhole914 in modified fusion cage 904.

As shown in FIG. 12C, since the articulating drill targeting device 1204rotates side-to-side around the center of insertion handle 1236 which isaligned with the center of fixation screwhole 914, then the articulatingdrill targeting device 1204 also rotates about the center of fixationscrewhole 914.

The articulating drill targeting device 1204 is thus unimpeded inrotating side-to-side while maintaining alignment of drill guide 1208with fixation screwhole 914. Articulating drill targeting device 1204easily maintains this alignment while rotating from the maximum leftguide pin trajectory 936, through arc 934, to the maximum right guidepin trajectory 938.

FIG. 12D shows a left side view and a cross-sectional view of the guidebody 1212. FIG. 12E shows the back view and FIG. 12F show the front viewof guide body 1212. The drill guide 1208 is able to slide up and down inhole 1258. A spring-loaded locking lever 1216 engages serrations 1209 inthe side of drill guide 1208. The geometry of this engagement is suchthat the drill guide 1208 can be pushed down, without impediment, firmlyinto position against the backbone 104 at the desired guide pin entrypoint 604 (e.g. FIG. 6).

The locking lever 1216 prevents the drill guide 1208 from backing up.The articulated drill targeting device 1204, therefore, remains firmlyin position by acting as a C-clamp in squeezing the L5 backbone 104between the modified fusion cage 904 and the drill guide 1208.

FIG. 12G shows an exploded perspective view of guide body 1212. A spring1215 fixed by pin 1218 maintains the top end 1217 of locking lever 1216to default to a raised position. The bottom end 1219 of locking lever1216 is thereby maintained depressed against the serrations 1209 on thedrill guide 1208 (e.g. FIG. 12D) until such time as the surgeondepresses the top end 1217 of the locking lever 1216.

Following insertion of the guide pin 504, the clamping action of thearticulated drill targeting device 1204 is released by the surgeondepressing the top end 1217 of the locking lever 1216 which rotates onpin 1218 to raise the bottom end 1219 away from the serrations 1209 ondrill guide 1208. The drill guide 1208 can now be pulled up out of thedrill body 1212 and off of the guide pin 504.

FIGS. 12D, 12F, and 12G show a guide pin exit slot 1262 connecting thefront side of the guide body 1212 with the drill guide hole 1258.Following removal of the drill guide 1208, the articulating drilltargeting device 1204 is rotated to the back allowing the guide pin 504to exit the drill guide hole 1258 by way of this guide pin exit slot1262. The articulating drill targeting device 1204 can now be removedalong with the inserter handle 1236 in the reverse order of theirattachment to modified fusion cage 904.

FIG. 12H shows the drill guide 1208 with an alignment fin or pin 1207that engages guide pin exit slot 1262 as drill guide 1208 slides up anddown through the hole 1258 in guide body 1212. Drill guide 1208 isthereby prevented from rotating in the hole 1258. The serrations 1209 onthe side of drill guide 1208 are thereby maintained facing and engaginglocking lever 1216.

FIG. 12H shows depth gauge markings 1210 and numbers 1211 on drill guide1208. When the drill guide 1208 is clamped into position against thebackbone 104 at the desired guide pin entry point 604 (e.g. FIG. 6), thedistance from the guide pin entry point 604 to the center of fixationscrewhole 914 in modified fusion cage 904 can be read off the drillguide 1208 where the depth gage markings 1210 align with the top ofguide body 1212.

Knowing the height of the selected modified fusion cage 904 and knowingthe desired distance that fixation screw 508 needs to extend past thiscage, the surgeon can easily calculate the required length of fixationscrew 508.

By knowing the required length of the fixation screw 508, the surgeonknows to what depth guide pin 504 must be drilled. Repeated use ofx-rays to follow the advance of guide pin 504 to the desired depth isnot required. Measuring the length of guide pin 504 thus inserted, inorder to determine the required length of fixation screw 508, is notnecessary. Thus, the previously described negative factors associatedwith the use of x-ray guidance are further avoided.

FIG. 12H shows a flexible guide pin tissue protector 1213 that can bescrewed onto or otherwise attached to drill guide 1208. This guide pintissue protector 1213 prevents important adjacent tissues from beingdamaged by winding around the spinning guide pin 504 as it is beingdrilled into the bone.

FIG. 12I shows a flexible screw insertion tissue protector 1266 that canbe slid over guide pin 504 following insertion of guide pin 504, removalof drill guide 1208, and removal of articulating drill targeting device1204. This flexible screw insertion tissue protector 1266 accommodatesthe passage of a flexible drill bit 1270. It also accommodates thepassage of fixation screw 508 and attached flexible screwdriver 1274down over guide pin 504. Adjacent soft tissues are thus protected fromdamage by the spinning drill bit 1270. Adjacent soft tissues are alsoprotected by the spinning fixation screw 508 and screwdriver 1274 duringscrew insertion.

A Potential Method for Implementing Various of the Preferred Embodiments

FIG. 13 depicts an example method 1300 for implementing various of theembodiments disclosed herein. This example method is applicable to bothmodified fusion cages 904 and 1004, and can be briefly summarized asfollows. Step 1304 comprises excising the diseased disc. Step 1308comprises trialing the disc space. Step 1312 comprises inserting themodified fusion cage. Step 1316 comprises positioning the drilltargeting device. Step 1320 comprises measuring for fixation screwlength. Step 1324 comprises pinning with the guide pin. Step 1328comprises removing the drill targeting device. Step 1332 comprisesscrewing in the fixation screw. Step 1336 comprises extracting the guidepin. Step 1340 comprises locking the fixation screw.

The method 1300 will now be described in more detail. FIG. 14 showsexcising the diseased disc 112 from between the backbones 104 and 108 tobe fused, thus creating a space 1404 for the cage.

FIG. 15 shows trialing the disc space by attaching the trial cage 404 toan insertion handle 1504. The varying sizes of modified trial cages arerepeatedly inserted into the disc space until a proper fit is obtained.

FIG. 16 shows inserting the modified fusion cage 904 into space 1404using an insertion handle 1236.

FIG. 17A shows positioning the rigid drill targeting device 1104 byinserting the drill target 1116 through the utility screwhole 920 toengage the front side of fixation screwhole 914. In such an environment,the rigid drill targeting device 1104 can now be rotated in theside-to-side direction and front-to-back direction to place the entrypoint for the guide pin 504 insertion at a position of the surgeon'schoosing, while maintaining the alignment of the drill guide 1108 withthe fixation screwhole 914 in the modified fusion cage 904.

FIGS. 17A and 17B show movement in the side-to-side direction. In FIG.17A the rigid drill targeting device 1104 has been rotated to the leftside to select an entry point 1704. In FIG. 17B the rigid drilltargeting device 1104 has been rotated to the right side to select adifferent entry point 1708. At either entry point, the drill guide 1108remains precisely aligned with the drill target 1116 and fixationscrewhole 914.

FIGS. 17C and 17D show movement in the front-to-back direction. In FIG.17C the rigid drill targeting device 1104 has been rotated toward thefront. In FIG. 17D the rigid drill targeting device 1104 has beenrotated toward the back. Rotation in this front-to-back direction iscarried out simultaneously with rotation in the side-to-side directionin order to place the drill guide 1108 at the entry point of thesurgeon's choosing.

In FIG. 17A the drill guide 1108 has been slid down against the bone atthe chosen entry point 1704 and locked in position with the thumbscrew1118 (e.g. FIG. 11A). The position of the drill targeting device isstabilized by the clamping of the backbone 104 between the drill guide1108 and drill target 1116.

FIG. 17E shows positioning the articulating drill targeting device 1204.The inserter handle 1236 is already in position having been used in step1312 inserting the modified fusion cage 904. The articulating drilltargeting device 1204 is now assembled onto insertion handle 1236 asdescribed in connection at least with FIGS. 12A and 12B.

As with the rigid drill targeting device 1104, the articulating drilltargeting device 1204 can now be rotated in the side-to-side directionand in the front-to-back direction to place the entry point for guidepin 504 insertion at a location of the surgeon's choosing, whilemaintaining the alignment of the drill guide 1208 with the fixationscrewhole 914 in the modified fusion cage 904.

FIGS. 17E and 17F show this movement in the side-to-side direction. InFIG. 17E the articulating drill targeting device 1204 is rotated to theleft side to select an entry point 1704. In FIG. 17F the articulatingdrill targeting device 1204 is rotated to the right side to select adifferent entry point 1708. At either entry point the drill guide 1208remains precisely aligned with the fixation screwhole 914.

FIGS. 17G and 17H show movement in the front-to-back direction. In FIG.17E the articulating drill targeting device 1204 has been rotated to thefront. In FIG. 17H the articulating drill targeting device 1204 has beenrotated to the back. Rotation in this front-to-back direction is carriedout simultaneously with rotation in the side-to-side direction in orderto place the drill guide 1208 at the entry point of the surgeon'schoosing.

In FIG. 17E the drill guide 1208 has been slid down against the bone atthe chosen entry point 1704 and is held locked in position by thelocking lever 1216, as described at least in connection with FIGS. 12D,12E, and 12F.

FIG. 18 shows measuring for fixation screw length by reading the valueof the depth gauge marking 1210 on drill guide 1208 that is aligned withthe top of guide body 1212 as described in connection at least with FIG.12H. The required depth of insertion of guide pin 504 is next calculatedas described in connection at least with FIG. 5 and determining therequired length of the fixation screw 508. The same procedure is usedwith the rigid drill targeting device 1104.

FIG. 19 shows pinning the modified fusion cage 904 with a guide pin 504using the articulating drill targeting device 1204. The guide pin 504 isinserted into the drill guide 1208 and drilled through the backbone 104on the near side of the modified fusion cage 904, through the fixationscrewhole 914 in the modified fusion cage 904, and then into thebackbone 108 on the far side of the modified fusion cage 904. The guidepin 504 is inserted to the predetermined depth calculated in step 1320.The same procedure is used with the rigid drill targeting device 1104.FIG. 19 shows the final position of guide pin 504.

FIG. 20 shows removing the articulating drill targeting device 1204 asdescribed in connection at least with FIGS. 12D, 12F, and 12G. The rigiddrill targeting device 1104 is removed from guide pin 504 in a similarfashion. Thumbscrew 1118 (e.g. FIG. 11A) is loosened. Drill guide 1108is slid up and off from the guide pin 504 and the rigid drill targetingdevice 1104 is rotated back and off from the guide pin 504 in a manneridentical to the articulating drill targeting device 1204. The drilltarget 1116 is then disengaged from fixation screwhole 914 and extractedout of the utility screwhole 920.

FIG. 21 shows screwing in the fixation screw 508. Depending on surgeonpreference, drilling over guide pin 504 using cannulated drill 1270(e.g. FIG. 12I) may first be performed. Fixation screw 508 is theninserted over guide pin 504 using the cannulated flexible screwdriver1274 (e.g. FIG. 12I). If the surgeon prefers, these steps can beperformed through the flexible screw insertion tissue protector 1266 asdescribed in connection at least with FIG. 12I.

FIG. 22 shows extracting the guide pin 504 leaving the fixation screw508 in its final position, thereby firmly fixing modified fusion cage904 in position between the L5 backbone 104 and the S1 backbone 108.

FIG. 23 shows locking the fixation screw 508 to the modified fusion cage904 by inserting locking screw 930 into utility screwhole 920 using forexample a hex screwdriver 2304.

Additional Information

The embodiments disclosed herein allow the accurate visualidentification of a variable entry point into bone, the accuratemechanical identification of a fixed screwhole in a fusion cagepositioned in a disc space, and the accurate control of the drill pathbetween these two points.

Repeated X-rays are not required to adjust trajectory as the guide pinis advanced. Radiation exposure to the patient and to the surgeon isthereby reduced.

The continuous presence of an X-ray machine in the operative field isnot required and therefore the surgeon's view of and access to theoperative site during a critical phase of the surgery are not blocked.

Repeated adjustments of the trajectory during drilling are not requiredthus avoiding deflection of the guide pin down a misdirected drill pathor drilling at a new entry point.

The ability to safely and accurately achieve bone fixation by placingthe screw through the cage in this fashion avoids alternative fixationmethods. These methods may involve making a separate incision. They mayinvolve closing the present incision and turning the patient over tomake a separate incision on the opposite side of the body. Avoiding therequirement to make a separate incision or to turn the patient overshortens the operative time for the patient and reduces the surgicalinsult to the patient.

A fusion cage may displace when a patient is turned over in theoperating room in order to put alternative fixation in through aseparate incision on the opposite side of the body. Fixing the cage withthe screw in this fashion at the same time and through the same incisionas the cage is placed avoids this risk of cage displacement.

The prominence of large implants used as an alternate fixation method onthe surface of the bone, which can irritate or injure adjacentstructures, is avoided.

A smaller diameter screwhole in the fusion cage results in a reduceddistance the cage can displace before being stopped by the side of thescrewhole contacting the screw.

A smaller diameter screwhole facilitates the design of a mechanism tolock the cage to the screw.

Having a fusion cage with a fenestration dedicated to the screw only andmade as small in diameter as the screw, avoids partial cagedisplacement, damage to the graft material by the screw, and maximizesthe area of remaining fenestrations for graft. This lessens the risk ofa loose cage which can lead to failure of fusion.

Passing the screw through such a small screwhole is only feasibleutilizing the drill targeting device.

The hourglass shape of the screwhole in modified cage 904 gives thesmallest diameter fixed screwhole that will allow screw entry frommultiple directions.

Connecting the utility screwhole to the center of the fixation screwholeallows the center of the screwhole to be accessed by the target of arigid drill targeting device. The targeting device can then rotate onthis center point allowing the guide pin to approach from variedtrajectories yet still direct the guide pin through the center of thescrewhole. This feature allows the use of a locking screw whichdecreases the risk of the fixation screw migrating in or backing out. Itfurther diminishes any movement between the cage and fixation screw.

The modified cage 1004 with the tilting, bearing, or snap ring fixationscrewhole allows the screwhole to be the same diameter as the fixationscrew while still permitting screw entry from multiple trajectories.Having the fixation screwhole the same diameter as the fixation screwprevents any undesired movement between the screw and cage. The snapring can act as a locking mechanism on the fixation screw so theseparate locking screw is not necessarily required. The metal tilting,bearing, or snap ring can protect the fusion cage, which is usually madeof plastic, from damage by the guide pin as it passes through thescrewhole. If the guide pin is slightly off center, it can deflect offthe metal bearing or snap ring rather than dig into the side wall of aplastic cage with the fixed hole.

Unlike previous cages, use of the x-ray machine is not required.Radiation exposure to the patient and operating room personnel isreduced. Surgeon and assistants having to move out of the way of thex-ray machine at the critical point in the operation is avoided. Theguide pin can be placed on the first pass. Multiple trajectory changesare avoided. The operation is performed faster. Not bringing the x-raymachine into the operative field and performing the operation fasterboth decrease the risk of wound contamination and infection, decreaseblood loss, and decrease expense of operating room time. No exceptionalhand-eye skills are necessary on the surgeon's part in order to drillthe guide pin through the cage.

The drill targeting device makes it possible to pass the guide pin onthe first attempt case after case. No trajectory adjustments arerequired. Deflection of the guide pin down a misdirected drill path isavoided. Restarting pin entry at a new entry site to avoid an old drillpath is not required. The rigid drill targeting device allows thesurgeon to select from multiple possible entry points. He can select theentry point that best avoids important adjacent anatomical structuresand at the same time pass the pin through the center of a minimumdiameter screwhole.

The articulated drill targeting device has the advantages of the rigid.In addition, the articulated has a wider unrestricted range of movementin the front-to-back direction. Since it is not necessary to pass anarrow targeting arm into the center of the cage, the risk of a benttarget arm misdirecting the guide pin is avoided. Since it is mounted tothe insertion handle which is screwed into the cage, the connection ofthe targeting device to the cage is secure. The risk of the targetingdevice disengaging from the cage and misdirecting a screw is avoided.The ratcheting locking lever on the drill guide allows the surgeon topush the drill guide down against the bone with one hand without havingto depress the locking lever. The drill guide is then firmly clampedonto the bone with the cage in the disc space on one end and the drillguide engaging the bone on the other. The locking lever will preventsthe targeting device from coming unclamped by the drill guideinadvertently backing up.

Incorporating a guide pin exit slot allows the targeting device to beremoved from the pin without sliding it up and off of the pin. At timesit is necessary for the guide pin to enter the abdominal wall through asmall incision separate from the larger incision in which the cage isplaced into the disc and through which the targeting device is attachedto the cage. The targeting device cannot be slid up and off of the pinin this circumstance. The guide pin exit slot makes it possible for theguide pin to be placed through this small separate incision yet stillmakes it possible for the surgeon to remove the targeting device fromthe pin.

The alignment pin on the side of the drill guide controls rotation ofthe drill guide in the guide block and keeps the serrations on the drillguide oriented facing the locking lever.

Having depth markings and numbers on the drill guide enables thetargeting device to double as a measuring caliper. The depth to whichthe guide pin should be inserted and the length of the fixation screwthat is required can be determined using this feature avoiding thenecessity of doing it with an x-ray as has been historically required.

The ability to pass a screw through a fusion cage through the sameincision on the front of the abdomen avoids having to make a separateincision on the back of the patient to insert other types of fixationscrews that join the bones together. Fewer incisions mean shorteroperative times, less blood loss, less risk of infection. Injury to theback muscles that occurs with this separate incision on the back isavoided. Displacement of the cage occurring when the patient is beingturned over to put screws in from the back is avoided.

It is anticipated that various changes may be made in the arrangementand operation of the system of the present invention without departingfrom the spirit and scope of the invention, as defined by the followingclaims.

What is claimed is:
 1. A spinal fusion system, comprising: anarticulated drill targeting device and a guide pin for positioning abone fixation screw in a centrally-located fixation screwhole in aspinal fusion cage, said fusion cage having a front, back, left side,right side, top, and bottom, said fixation screwhole extending from topto bottom of said fusion cage, said fixation screwhole having a center,said fixation screw positionable in said fixation screwhole at an anglevariable side-to-side and front-to-back up to a maximum angle, saidarticulated drill targeting device having a linkage mechanism in theform of two overlapping, dependently-linked parallelograms, eachparallelogram having two horizontal sides and two vertical sides, wherethe four sides of each parallelogram are linked at the corners by hingepins, where the angle between the sides of each parallelogram arethereby variable, where the two vertical sides of a first parallelogramoverlap the two horizontal sides of a second parallelogram atintersections, where said overlapped sides of said parallelograms arelinked at said intersections by four hinge pins, where the angularvariation of said first parallelogram thereby produces an identicalangular variation of said second parallelogram, where one horizontalside of said first parallelogram is an inserter body, an inserter handlehaving a center which passes through said inserter body, where saidspinal fusion cage is attached to said inserter handle, where saidcenter of said fixation screwhole and said center of said inserterhandle are aligned with said horizontal side of said firstparallelogram, where said inserter body rotates on said inserter handleside-to-side in relation to said spinal fusion cage, where one verticalside of said second parallelogram is a guide body, and a drill guidehaving a center passes through said guide body, said center of saidfixation screwhole and said center of said drill guide are aligned withsaid vertical side of said second parallelogram, where the remainingsides of said first and said second parallelograms are linkage arms,where said first and second parallelograms are angulated front-to-backin relation to said spinal fusion cage, where alignment of said centerof said drill guide with said center of said fixation screwhole ismaintained with said front-to-back angulation of said first and secondparallelograms, whereby said drill guide directs said guide pin throughsaid center of said fixation screwhole in said fusion cage, whereby saidfixation screw is positioned in said fixation screwhole at an anglevariable side-to-side and front-to-back in relation to said fusion cage.2. The system of claim 1, wherein a longitudinal axis of the inserterhandle aligns with a center of a fixation screwhole in said fusion cage.3. The system of claim 1, further comprising: the drill guide mounted ina drill guide hole in said guide body adjacent to the end of saidtargeting device.
 4. The system of claim 1, wherein said drill guide isaligned to direct said guide pin at the center of said fixationscrewhole in said fusion cage when the guide pin is inserted in thedrill guide.
 5. The system of claim 1, wherein rotation of said inserterbody on said inserter handle permitting the side-to-side variation in atrajectory of the guide pin while maintaining alignment of said guidepin with the center of said fixation screwhole in said spinal fusioncage, and further wherein said interconnected parallelogram of saidarticulating linkage permits the front-to-back variation in thetrajectory of said guide pin while maintaining alignment of said guidepin with the center of said fixation screwhole in said spinal fusioncage.
 6. The system of claim 1 wherein a guide pin exit slot connectsone side of said guide body with a drill guide hole.
 7. The system ofclaim 1 wherein a spring-loaded locking lever on said guide body engagesbeveled serrations on said drill guide, thereby allowing said drillguide to ratchet toward said spinal fusion cage while preventingmovement of the drill guide away from said fusion cage.